Arthroplasty (surgical reformation) of the elbow joint is of major interest at the present time and has been generated by several factors:
(1) Resection and interposition arthroplasty of the elbow have failed to predictably relieve pain and provide the necessary motion and stability;
(2) Arthrodesis of the elbow is a disabiling procedure. Arthrodesis compromises the ability to position the hand in space. Regardless of the position selected for arthrodesis, many of the functional skills of the upper extremity are sacrificed.
(3) The initial types of total elbow prostheses have an unacceptable incidence of complications. Clinical trials with existing designs (stem-fixed, hinged prostheses) have shown a marked tendency toward loosening of the prosthetic components. Souter reported that 17 of 25 Dee prostheses (68%) loosened with a follow-up from 14-40 months. Most reports also contain a significant incidence of other complications including skin sloughs, wound breakdown, fractures, infections, and nerve palsies. These complications have been attributed to the constrained hinge design of these prostheses and to the bulk of the prostheses. There has recently been reported a replacement prosthesis requiring the excision of the trochlea. The prosthesis itself is of biconical bearing surface design, the ends of which are fixed into the humeral epicondyles.
This design has certain potential drawbacks. Among these are, firstly, replacement prostheses, in general, have an increased incidence of complications as compared to resurfacing procedures. Secondly, the bioconical design does not permit side to side play under varus-valgus stress in the joint, and such stress will contribute to loosening of the anchoring points of the prosthesis. Thirdly, substantial bone resection is required and, in the event that arthrodesis of the joint is later desired, this procedure would be difficult. Fourthly, the lateral stability of the joint is impaired because the radial head is excised. Fifth, the articulating surface of revolution between the humeral and ulnar components of this prosthesis is limited.
There has also been recently reported an elbow prosthesis in which the humeral and ulnar components have limited articulation over a longitudinally convex, circular (i.e., partly cylindrical) bearing surface. This cylindrical design does not prevent lateral (i.e., side to side) slippage under varus-valgus stress imposed on the prosthesis. Further, the articular bearing surface of the ulnar component is substantially less than the 175.degree.-180.degree. bearing surface of the normal ulna.
It is a major objective of this invention to overcome the disadvantages of the prior art devices as well as those of the structure first described above and to attempt to attain the ideal prosthesis design for an elbow joint. The ideal prosthesis for the elbow joint should have rotatably articulating bearing surfaces of 175.degree.-180.degree. to simulate the normal elbow flexion and extension characteristics, should have a means to efficiently resist side to side movement under varus-valgus stress imposed on the elbow joint and should also be designed to provide improved resistance to compressive axial loading, and should avoid bone resection to the greatest possible extent. The invention herein is designed with the foregoing as primary objectives. Other advantages of the design of this invention will become apparent from the summary and description hereinafter set forth.